1. Field of the Invention
The invention relates to a circuit board and a manufacturing method thereof, and particularly relates to a circuit board with preferable wire bonding and soldering capabilities and a manufacturing method thereof.
2. Description of Related Art
The conventional surface treatment layer for pads, such as an electroless plating nickel-palladium-gold layer, is formed by respectively depositing an electroless plating nickel layer, an electroless plating palladium layer, and an immersion plating gold layer on a surface of a copper pad. Alternatively, an electroless plating palladium-gold layer, is formed by respectively depositing an electroless plating palladium layer and an immersion plating gold layer on a surface of a copper pad. Such surface treatment layer normally provides a wire bonding capability and a soldering capability.
Recently, some studies indicate that an electroless plating nickel-palladium-gold layer or electroless plating palladium-gold layer that includes a pure electroless plating palladium layer or a phosphorous-less electroless plating palladium layer has a wire bonding capability slightly better than that of an electroless plating nickel-palladium-gold layer or electroless plating palladium-gold layer that includes a phosphorous-containing electroless plating palladium layer. However, the electroless plating nickel-palladium-gold layer or electroless plating palladium-gold layer that includes a phosphorous-containing electroless plating palladium layer has a soldering capability slightly better than that of the electroless plating nickel-palladium-gold layer or electroless plating palladium-gold layer that includes a phosphorous-less electroless plating palladium layer. When a product requires a preferable wire bonding capability and a preferable soldering capability at the same time, the differences in wire bonding and soldering capabilities between the electroless plating nickel-palladium-gold layer or electroless plating palladium-gold layer that includes a phosphorous-containing electroless plating palladium layer and the electroless plating nickel-palladium-gold layer or electroless plating palladium-gold layer that includes a phosphorous-less electroless plating palladium layer may cause disturbance in choosing suitable materials. Thus, how to provide the preferable wire bonding and soldering capabilities at the same time in a product is certainly an issue to work on.